F. Niculescu et al., RECEPTOR-INDEPENDENT ACTIVATION OF GUANINE-NUCLEOTIDE-BINDING REGULATORY PROTEINS BY TERMINAL COMPLEMENT COMPLEXES, The Journal of biological chemistry, 269(6), 1994, pp. 4417-4423
Activation of heterotrimeric guanine nucleotide-binding proteins (G pr
oteins) by terminal complement complexes (TCC) was investigated on hum
an lymphoblastoid B-cell line JY25 and its mutant JY5 deficient in gly
cosylphosphatidylinositol-anchored proteins. TCC assembly achieved by
antibody dependent activation of C7-deficient serum reconstituted with
C7 increased specific guanosine-5'-(gamma-thio)triphosphate (GTP gamm
a S) binding, 4- and 8-fold, in JY25 and JY5 membranes, respectively,
between 2 and 10 min, over the level without C7. TCC also increased GT
Pase activity 5- and 4-fold in JY25 and JY5, respectively, between 5 a
nd 10 min. Increased GTPase activity was noted first with C5b-7 assemb
ly, which increased further with C5b-8 and C5b-9. The presence of G pr
oteins in anti TCC immunoprecipitates of cell lysates was investigated
by demonstration of Ga subunit that can be ADP-ribosylated by pertuss
is toxin (PTX). Immunoprecipitated TCC complexes contained a PTX-sensi
tive 41-kDa Gi alpha/Go alpha subunit, as shown by SDS PAGE and Wester
n blotting. These complexes were functionally active as determined by
GTP gamma S binding. We have further shown that enhanced TCC eliminati
on from the plasma membrane induced by TCC-generated signals was inhib
ited by PTX. In conclusion the biological activities induced by TCC in
nucleated cells may be mediated in part by activation of PTX-sensitiv
e G proteins.